Code division multiplexing in a single-carrier frequency division multiple access system

ABSTRACT

In a single-carrier frequency division multiple access (SC-FDMA) system that utilizes interleaved FDMA (IFDMA) or localized FDMA (LFDMA), a transmitter generates modulation symbols for different types of data (e.g., traffic data, signaling, and pilot) and performs code division multiplexing (CDM) on at least one data type. For example, the transmitter may apply CDM on signaling and/or pilot sent on frequency subbands and symbol periods that are also used by at least one other transmitter. To apply CDM to a given data type (e.g., signaling), the transmitter performs spreading on the modulation symbols for that data type with an assigned spreading code. CDM may be applied across symbols, samples, samples and symbols, frequency subbands, and so on. The transmitter may perform scrambling after the spreading. The transmitter generates SC-FDMA symbols of the same or different symbol durations for traffic data, signaling, and pilot and transmits the SC-FDMA symbols.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present application for patent is a continuation of Non-Provisional application Ser. No. 11/431,969 entitled “CODE DIVISION MULTIPLEXING IN A SINGLE-CARRIER FREQUENCY DIVISION MULTIPLE ACCESS SYSTEM” filed May 10, 2006 which claims priority to Provisional Application No. 60/706,639 entitled “CODE DIVISION MULTIPLEXING IN A SINGLE-CARRIER FREQUENCY DIVISION MULTIPLE ACCESS SYSTEM” filed Aug. 8, 2005, and Ser. No. 60/710,503 entitled “CODE DIVISION MULTIPLEXING IN A SINGLE-CARRIER FREQUENCY DIVISION MULTIPLE ACCESS SYSTEM” filed Aug. 22, 2005, and Ser. No. 60/710,428 entitled “CODE DIVISION MULTIPLEXING IN A SINGLE-CARRIER FREQUENCY DIVISION MULTIPLE ACCESS SYSTEM” filed Aug. 22, 2005, all assigned to the assignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and more specifically to transmission techniques in a wireless communication system.

II. Background

A multiple-access system can concurrently communicate with multiple terminals on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. Multiple terminals may simultaneously transmit data on the reverse link and/or receive data on the forward link. This is often achieved by multiplexing the multiple data transmissions on each link to be orthogonal to one another in time, frequency and/or code domain. For example, data transmissions for different terminals may be orthogonalized by using different orthogonal codes in a code division multiple access (CDMA) system, by transmitting in different time slots in a time division multiple access (TDMA) system, and by transmitting on different frequency subbands in a frequency division multiple access (FDMA) system or an orthogonal frequency division multiple access (OFDMA) system.

The terminals may transmit various types of data such as, e.g., traffic data, signaling, and pilot. Traffic data refers to data sent by an application (e.g., voice or packet data), signaling refers to data sent to support system operation (e.g., control data), and pilot refers to data that is known a priori by both a transmitter and a receiver. The different types of data may have different requirements and may be transmitted in different manners, e.g., at different rates and in different time intervals. Since signaling and pilot represent overhead, it is desirable for the terminals to transmit signaling and pilot as efficiently as possible.

There is therefore a need in the art for efficient transmission techniques in a multiple-access system.

SUMMARY

Techniques to efficiently transmit different types of data in a single-carrier frequency division multiple access (SC-FDMA) system are described herein. The SC-FDMA system may utilize (1) interleaved FDMA (IFDMA) to transmit on frequency subbands that are distributed across a frequency band or overall system bandwidth (2) localized FDMA (LFDMA) to transmit on a group of adjacent subbands, or (3) enhanced FDMA (EFDMA) to transmit data and pilot on multiple groups of adjacent subbands. IFDMA is also called distributed FDMA, and LFDMA is also called narrowband FDMA, classical FDMA, and FDMA.

In an embodiment, a transmitter (e.g., a terminal) generates modulation symbols for different types of data (e.g., traffic data, signaling, and pilot) and performs code division multiplexing (CDM) on one or more data types. CDM may be applied to traffic data, signaling, pilot, or any combination thereof. For example, the transmitter may apply CDM on signaling and/or pilot sent on frequency subbands and symbol periods that are also used by at least one other transmitter. To apply CDM to a given data type (e.g., signaling), the transmitter performs spreading on the modulation symbols for that data type with an assigned spreading code (e.g., a Walsh code). CDM may be applied across symbols, across samples, across both samples and symbols, across frequency subbands, and so on, as described below. The transmitter may also perform scrambling after the spreading. The transmitter generates SC-FDMA symbols of the same or different symbol durations for traffic data, signaling, and pilot and transmits the SC-FDMA symbols to a receiver. The receiver performs the complementary processing to recover the transmitted data.

Various aspects and embodiments of the invention are described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout.

FIG. 1 shows a system with multiple transmitters and a receiver.

FIG. 2A shows an exemplary subband structure for IFDMA.

FIG. 2B shows an exemplary subband structure for LFDMA.

FIG. 2C shows an exemplary subband structure for EFDMA.

FIG. 3A shows the generation of an IFDMA, LFDMA or EFDMA symbol.

FIG. 3B shows the generation of an IFDMA symbol.

FIG. 4 shows a frequency hopping (FH) scheme.

FIG. 5 shows a transmission scheme with CDM across symbols.

FIG. 6 shows transmissions for two transmitters with 2-chip spreading codes.

FIG. 7 shows a transmission scheme with CDM across samples.

FIG. 8 shows a transmission scheme with CDM across samples and symbols.

FIG. 9 shows use of different symbol durations for different types of data.

FIG. 10 shows a process for transmitting SC-FDMA symbols with CDM.

FIG. 11 shows a process for receiving SC-FDMA symbols sent with CDM.

FIG. 12 shows a block diagram of a transmitter.

FIG. 13 shows a block diagram of a receiver.

FIG. 14 shows a block diagram of a receive (RX) spatial processor.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

The transmission techniques described herein may be used for various communication systems. For example, these techniques may be used for an SC-FDMA system that utilizes IFDMA, LFDMA, or EFDMA, an OFDMA system that utilizes orthogonal frequency division multiplexing (OFDM), other FDMA systems, other OFDM-based systems, and so on. Modulation symbols are sent in the time domain with IFDMA, LFDMA, and EFDMA and in the frequency domain with OFDM. In general, the techniques may be used for a system that utilizes one or more multiplexing schemes for the forward and reverse links. For example, the system may utilize (1) SC-FDMA (e.g., IFDMA, LFDMA or EFDMA) for both the forward and reverse links (2) one version of SC-FDMA (e.g., LFDMA) for one link and another version of SC-FDMA (e.g., IFDMA) for the other link, (3) SC-FDMA for the reverse link and OFDMA for the forward link, or (4) some other combination of multiplexing schemes. SC-FDMA, OFDMA, some other multiplexing scheme, or a combination thereof may be used for each link to achieve the desired performance. For example, SC-FDMA and OFDMA may be used for a given link, with SC-FDMA being used for some subbands and OFDMA being used on other subbands. It may be desirable to use SC-FDMA on the reverse link to achieve lower PAPR and to relax the power amplifier requirements for the terminals. It may be desirable to use OFDMA on the forward link to potentially achieve higher system capacity.

The techniques described herein may be used for the forward and reverse links. The techniques may also be used for (1) an orthogonal multiple-access system in which all users within a given cell or sector are orthogonal in time, frequency and/or code and (2) a quasi-orthogonal multiple-access system in which multiple users within the same cell or sector may transmit simultaneously on the same frequency at the same time. A quasi-orthogonal SC-FDMA system supports space division multiple access (SDMA), which uses multiple antennas located at different points in space to support simultaneous transmissions for multiple users.

FIG. 1 shows an SC-FDMA system 100 with multiple (M) transmitters 110 a through 110 m and a receiver 150. For simplicity, each transmitter 110 is equipped with a single antenna 134, and receiver 150 is equipped with multiple (R) antennas 152 a through 152 r. For the reverse link, each transmitter 110 may be part of a terminal, and receiver 150 may be part of a base station. For the forward link, each transmitter 110 may be part of a base station, and receiver 150 may be part of a terminal. A base station is generally a fixed station and may also be called a base transceiver system (BTS), an access point, or some other terminology. A terminal may be fixed or mobile and may be a wireless device, a cellular phone, a personal digital assistant (PDA), a wireless modem card, and so on.

At each transmitter 110, a transmit (TX) data and pilot processor 120 encodes, interleaves, symbol maps traffic data and signaling and generates data symbols. The same or different coding and modulation schemes may be used for traffic data and signaling, which are collectively referred to as “data” in portions of the description below. Processor 120 also generates pilot symbols and multiplexes the data symbols and pilot symbols. As used herein, a data symbol is a modulation symbol for data, a pilot symbol is a modulation symbol for pilot, a modulation symbol is a complex value for a point in a signal constellation (e.g., for PSK or QAM), and a symbol is a complex value. A TX CDM processor 122 performs spreading for each type of data to be transmitted with CDM. An SC-FDMA modulator 130 performs SC-FDMA modulation (e.g., for IFDMA, LFDMA, or EFDMA) and generates SC-FDMA symbols. An SC-FDMA symbol may be an IFDMA symbol, an LFDMA symbol, or an EFDMA symbol. A data SC-FDMA symbol is an SC-FDMA symbol for data, and a pilot SC-FDMA symbol is an SC-FDMA symbol for pilot. A transmitter unit (TMTR) 132 processes (e.g., converts to analog, amplifies, filters, and frequency upconverts) the SC-FDMA symbols and generates a radio frequency (RF) modulated signal, which is transmitted via antenna 134.

At receiver 150, R antennas 152 a through 152 r receive the RF modulated signals from transmitters 110 a through 110 m, and each antenna provides a received signal to an associated receiver unit (RCVR) 154. Each receiver unit 154 conditions (e.g., filters, amplifies, frequency downconverts, and digitizes) its received signal and provides input samples to an associated demultiplexer (Demux) 156. Each demultiplexer 156 provides input samples for SC-FDMA symbols sent with CDM to an SC-FDMA demodulator (Demod) 160 and provides input samples for SC-FDMA symbols sent without CDM to an RX spatial processor 170. SC-FDMA demodulator 160 performs SC-FDMA demodulation on the input samples and provides received symbols. An RX CDM processor 162 performs the complementary despreading and provides detected data symbols. An RX data processor 164 processes the detected data symbols to recover the data sent with CDM.

RX spatial processor 170 performs receiver spatial processing for each subband used by multiple transmitters and separates out the data symbols sent by these transmitters. RX spatial processor 170 also demultiplexes the detected SC-FDMA symbols for each transmitter. An SC-FDMA demodulator 172 performs SC-FDMA demodulation on the detected SC-FDMA symbols for each transmitter and provides data symbol estimates for that transmitter, which are estimates of the data symbols sent by the transmitter. An RX data processor 174 symbol demaps, deinterleaves, and decodes the data symbol estimates for each transmitter and provides decoded data for that transmitter. In general, the processing by receiver 150 is complementary to the processing by transmitters 110 a through 110 m.

Controllers 140 a through 140 m and controller 180 direct the operation of various processing units at transmitters 110 a through 110 m and receiver 150, respectively. Memories 142 a through 142 m and memory 182 store program codes and data for transmitters 110 a through 110 m and receiver 150, respectively.

System 100 may utilize IFDMA, LFDMA, or EFDMA for transmission. The subband structures and symbol generation for IFDMA, LFDMA, and EFDMA are described below.

FIG. 2A shows an exemplary subband structure 200 for IFDMA. The overall system bandwidth of BW MHz is partitioned into multiple (K) orthogonal subbands that are given indices of 1 through K, where K may be any integer value. The spacing between adjacent subbands is BW/K MHz. For simplicity, the following description assumes that all K total subbands are usable for transmission. For subband structure 200, the K subbands are arranged into S disjoint or non-overlapping interlaces. The S interlaces are disjoint in that each of the K subbands belongs in only one interlace. In an embodiment, each interlace contains N subbands that are uniformly distributed across the K total subbands, consecutive subbands in each interlace are spaced apart by S subbands, and interlace u contains subband u as the first subband, where K=S·N and uε{1, . . . , S}. In general, a subband structure may include any number of interlaces, each interlace may contain any number of subbands, and the interlaces may contain the same or different numbers of subbands. Furthermore, N may or may not be an integer divisor of K, and the N subbands may or may not be uniformly distributed across the K total subbands.

FIG. 2B shows an exemplary subband structure 210 for LFDMA. For subband structure 210, the K total subbands are arranged into S non-overlapping groups. In an embodiment, each group contains N subbands that are adjacent to one another, and group v contains subbands (v−1)·N+1 through v·N, where v is the group index and vε{1, . . . , S}. N and S for subband structure 210 may be the same or different from N and S for subband structure 200. In general, a subband structure may include any number of groups, each group may contain any number of subbands, and the groups may contain the same or different numbers of subbands.

FIG. 2C shows an exemplary subband structure 220 for EFDMA. For subband structure 220, the K total subbands are arranged into S non-overlapping sets, with each set including G groups of subbands. In an embodiment, the K total subbands are distributed to the S sets as follows. The K total subbands are first partitioned into multiple frequency ranges, with each frequency range containing K′=K/G consecutive subbands. Each frequency range is further partitioned into S groups, with each group including V consecutive subbands. For each frequency range, the first V subbands are allocated to set 1, the next V subbands are allocated to set 2, and so on, and the last V subbands are allocated to set S. Set s, for s=1, . . . , S, includes subbands having indices k that satisfy the following: (s−1)·V≦k modulo (K/G)<s·V. Each set contains G groups of V consecutive subbands, or a total of N=G·V subbands. In general, a subband structure may include any number of sets, each set may contain any number of groups and any number of subbands, and the sets may contain the same or different numbers of subbands. For each set, the groups may contain the same or different numbers of subbands and may be distributed uniformly or non-uniformly across the system bandwidth.

An SC-FDMA system may also utilize a combination of IFDMA, LFDMA, and/or EFDMA. For example, multiple interlaces may be formed for each subband group, and each interlace may be allocated to one or more users for transmission. As another example, multiple subband groups may be formed for each interlace, and each subband group may be allocated to one or more users for transmission. IFDMA, LFDMA, EFDMA, and variants and combinations thereof may be considered as different versions of SC-FDMA. In general, the techniques described herein may be used for any subband structure with any number of subband sets and where each subband set may include any number of subbands that may be arranged in any manner. For each subband set, (1) the subbands may be individually and either uniformly or non-uniformly distributed across the system bandwidth, (2) the subbands may be adjacent to one another in one group, or (3) the subbands may be distributed in multiple groups, where each group may be located anywhere in the system bandwidth and may contain one or multiple subbands.

FIG. 3A shows the generation of an IFDMA symbol for one interlace, an LFDMA symbol for one subband group, or an EFDMA symbol for one subband set. An original sequence of N modulation symbols to be transmitted in one symbol period on the interlace, subband group, or subband set is denoted as {d₁, d₂, d₃, . . . , d_(N)} (block 310). The original sequence is transformed to the frequency domain with an N-point discrete Fourier transform (DFT) to obtain a sequence of N frequency-domain values (block 312). The N frequency-domain values are mapped onto the N subbands used for transmission, and K−N zero values are mapped onto the remaining K−N subbands to generate a sequence of K values (block 314). The N subbands used for transmission are in one group of adjacent subbands for LFDMA (as shown in FIG. 3A), are in one interlace with subbands distributed across the K total subbands for IFDMA (not shown in FIG. 3A), and are one in set of multiple groups of subbands for EFDMA (also not shown in FIG. 3A). The sequence of K values is then transformed to the time domain with a K-point inverse discrete Fourier transform (IDFT) to obtain a sequence of K time-domain output samples (block 316).

The last C output samples of the sequence are copied to the start of the sequence to form an IFDMA, LFDMA, or EFDMA symbol that contains K+C output samples (block 318). The C copied output samples are often called a cyclic prefix or a guard interval, and C is the cyclic prefix length. The cyclic prefix is used to combat intersymbol interference (ISI) caused by frequency selective fading, which is a frequency response that varies across the system bandwidth.

FIG. 3B shows the generation of an IFDMA symbol for one interlace for the case in which N is an integer divisor of K and the N subbands are uniformly distributed across the K total subbands. An original sequence of N modulation symbols to be transmitted in one symbol period on the N subbands in interlace u is denoted as f{d₁, d₂, d₃, . . . , d_(N)} (block 350). The original sequence is replicated S times to obtain an extended sequence of K modulation symbols (block 352). The N modulation symbols are sent in the time domain and collectively occupy N subbands in the frequency domain. The S copies of the original sequence result in the N occupied subbands being spaced apart by S subbands, with S−1 subbands of zero power separating adjacent occupied subbands. The extended sequence has a comb-like frequency spectrum that occupies interlace 1 in FIG. 2A.

The extended sequence is multiplied with a phase ramp to obtain a frequency-translated sequence of K output samples (block 354). Each output sample in the frequency-translated sequence may be generated as follows: x _(n) =d _(n) ·e ^(−j2π·(n−1)·(u−1)/K), for n=1, . . . , K,  Eq (1) where d_(n) is the n-th modulation symbol in the extended sequence, x_(n) the n-th output sample in the frequency-translated sequence, and u is the index of the first subband in the interlace. The multiplication with the phase ramp e^(−j2π·(n−1)·(u−1)/K·) in the time domain results in the frequency-translated sequence occupying interlace u in the frequency domain. The last C output samples of the frequency-translated sequence are copied to the start of the frequency-translated sequence to form an IFDMA symbol that contains K+C output samples (block 356).

The processing shown in FIG. 3A may be used to generate IFDMA, LFDMA and EFDMA symbols for any values of N and K. The processing shown in FIG. 3B may be used to generate an IFDMA symbol for the case in which N is an integer divisor of K and the N subbands are uniformly distributed across the K total subbands. The IFDMA symbol generation in FIG. 3B does not require a DFT or an IDFT and may thus be used whenever possible. IFDMA, LFDMA and EFDMA symbols may also be generated in other manners.

The K+C output samples of an SC-FDMA symbol (which may be an IFDMA, LFDMA or EFDMA symbol) are transmitted in K+C sample periods, one output sample in each sample period. An SC-FDMA symbol period (or simply, a symbol period) is the duration of one SC-FDMA symbol and is equal to K+C sample periods. A sample period is also called a chip period.

As generically used herein, a subband set is a set of subbands, which may be an interlace for IFDMA, a subband group for LFDMA, or a set of multiple subband groups for EFDMA. For the reverse link, S users may simultaneously transmit on S subband sets (e.g., S interlaces or S subband groups) to a base station without interfering with one another. For the forward link, the base station may simultaneously transmit on the S subband sets to S users without interference.

FIG. 4 shows a frequency hopping (FH) scheme 400 that may be used for the forward and/or reverse link. Frequency hopping can provide frequency diversity and interference randomization. With frequency hopping, a user may be assigned a traffic channel that is associated with a hop pattern that indicates which subband set(s), if any, to use in each time slot. A hop pattern is also called an FH pattern or sequence, and a time slot is also called a hop period. A time slot is the amount of time spent on a given subband set and typically spans multiple symbol periods. The hop pattern may pseudo-randomly select different subband sets in different time slots.

In an embodiment, one channel set is defined for each link. Each channel set contains S traffic channels that are orthogonal to one another so that no two traffic channels map to the same subband set in any given time slot. This avoids intra-cell/sector interference among users assigned to traffic channels in the same channel set. Each traffic channel is mapped to a specific sequence of time-frequency blocks based on the hop pattern for that traffic channel. A time-frequency block is a specific set of subbands in a specific time slot. For this embodiment, up to S users may be assigned the S traffic channels and would be orthogonal to one another. Multiple users may also be assigned the same traffic channel, and these overlapping users would share the same sequence of time-frequency blocks.

In another embodiment, multiple channel sets may be defined for each link. Each channel set contains S orthogonal traffic channels. The S traffic channels in each channel set may be pseudo-random with respect to the S traffic channels in each of the remaining channel sets. This randomizes interference among users assigned with traffic channels in different channel sets.

FIG. 4 shows an exemplary mapping of traffic channel 1 to a sequence of time-frequency blocks. Traffic channels 2 through S may be mapped to vertically and circularly shifted versions of the time-frequency block sequence for traffic channel 1. For example, traffic channel 2 may be mapped to subband set 2 in time slot 1, subband set 5 in time slot 2, and so on.

In general, multiple users may overlap in a deterministic manner (e.g., by sharing the same traffic channel), a pseudo-random manner (e.g., by using two pseudo-random traffic channels), or a combination of both.

With quasi-orthogonal SC-FDMA, multiple transmitters may transmit on a given time-frequency block. Traffic data, signaling, and/or pilot for these transmitters may be multiplexed using CDM, time division multiplexing (TDM), frequency division multiplexing (FDM), localized frequency division multiplexing (LFDM), and/or some other multiplexing scheme.

FIG. 5 shows a transmission scheme 500 with CDM applied across symbols. Multiple (Q) transmitters are mapped to the same time-frequency block and are assigned Q different spreading codes. The spreading codes may be Walsh codes, OVSF codes, orthogonal codes, pseudo-random codes, and so on. Each spreading code is a sequence of L chips that is denoted as {c₁, c₂, . . . , c_(L)}, where L≧Q. CDM may be applied on either (1) the modulation symbols prior to SC-FDMA modulation or (2) the SC-FDMA symbols after SC-FDMA modulation. For CDM prior to SC-FDMA modulation, a sequence of modulation symbols {d_(t,1), d_(t,2), . . . , d_(t,N)} is replicated L times, and the L replicated sequences are multiplied with the L chips of an assigned spreading code to generate L sequences of scaled modulation symbols. An SC-FDMA symbol is then generated for each sequence of scaled modulation symbols and transmitted in one symbol period. For CDM after SC-FDMA modulation, an SC-FDMA symbol X_(t) containing K+C output samples is replicated L times, and the L replicated SC-FDMA symbols are multiplied with the L chips of the spreading code to generate L scaled SC-FDMA symbols X_(t)·c₁ through X_(t)·c_(L), which are transmitted in L symbol periods.

For the example shown in FIG. 5, the first SC-FDMA symbol X₁ is multiplied with the L chips c₁ through c_(L) and transmitted in symbol periods 1 through L, the next SC-FDMA symbol X₂ is multiplied with the L chips C₁ through c_(L) and transmitted in symbol periods L+1 through 2L, and so on. Each SC-FDMA symbol X_(t) may be for traffic data, signaling, pilot, or a combination thereof.

For CDM across symbol periods, the wireless channel is assumed to be static over the L symbol periods used to transmit an SC-FDMA symbol. To recover SC-FDMA symbol X_(t), the receiver multiplies the L scaled SC-FDMA symbols received for that SC-FDMA symbol with the L chips of the assigned spreading code. The receiver then accumulates the L resultant SC-FDMA symbols to obtain a received SC-FDMA symbol for SC-FDMA symbol X_(t).

FIG. 6 shows exemplary transmissions for two transmitters with 2-chip spreading codes. For the example shown in FIG. 6, each transmitter transmits signaling in symbol periods 1 and 2, then traffic data in symbol periods 3 through t−1, then pilot in symbol periods t and t+1, then traffic data in symbol periods t+2 through T. Each transmitter generates SC-FDMA symbols in the normal manner, e.g., as shown in FIG. 3A or 3B. Transmitter 1 is assigned a spreading code of {+1, +1}, multiplies the SC-FDMA symbol for signaling with +1 and +1 to generate two scaled SC-FDMA symbols, and transmits these two scaled SC-FDMA symbols in symbol periods 1 and 2. Transmitter 1 also multiplies the SC-FDMA symbol for pilot with +1 and +1 to generate two scaled SC-FDMA symbols and transmits these two scaled SC-FDMA symbols in symbol periods t and t+1. Transmitter 2 is assigned a spreading code of {+1, −1}, multiplies the SC-FDMA symbol for signaling with +1 and −1 to generate two scaled SC-FDMA symbols, and transmits these two scaled SC-FDMA symbols in symbol periods 1 and 2. Transmitter 2 also multiplies the SC-FDMA symbol for pilot with +1 and −1 to generate two scaled SC-FDMA symbols and transmits these two scaled SC-FDMA symbols in symbol periods t and t+1. For the example shown in FIG. 6, transmitters 1 and 2 transmit SC-FDMA symbols for traffic data without CDM.

FIG. 6 shows transmission of traffic data, signaling, and pilot in one time-frequency block. In general, any type of data may be transmitted in a given time-frequency block. For example, traffic data and pilot may be transmitted in each time-frequency block assigned to a transmitter, and signaling may be transmitted as needed, e.g., periodically in every j-th time-frequency block, where j may be any integer value.

FIG. 7 shows a transmission scheme 700 with CDM applied across samples. D modulation symbols may be sent on one set of N subbands in one symbol period, where D≧1 and D may or may not be an integer divisor of N. Each modulation symbol may be for traffic data, signaling, or pilot. Each modulation symbol is replicated L times, and the L replicated symbols are multiplied with the L chips of the assigned spreading code to generate L scaled modulation symbols. For simplicity, FIG. 7 shows the transmission of one SC-FDMA symbol in one symbol period, with D being an integer divisor of N, or D=N/L. The first modulation symbol d₁ is multiplied with the L chips c₁ through c_(L) to obtain L scaled modulation symbols s₁=d₁·c₁ through s_(L)=d₁·c_(L), the next modulation symbol d₂ is multiplied with the L chips c₁ through c_(L) to obtain L modulation symbols s_(L+1)=d₂·c₁ through s_(2L)=d₂·c_(L), and so on, and the last modulation symbol d_(N/L), is multiplied with the L chips c₁ through c_(L) to obtain L scaled modulation symbols s_(N−L+1)=d_(N/L)·c₁ through s_(N)=d_(N/L)·c_(L). An SC-FDMA symbol may be generated based on the N scaled modulation symbols s₁ through s_(N). If L=N, then one modulation symbol is sent across all N samples in a symbol period.

To recover a given modulation symbol d_(n), the receiver multiplies the L scaled modulation symbols received for that modulation symbol with the L chips of the assigned spreading code. The receiver then accumulates the L resultant symbols to obtain a received modulation symbol for modulation symbol d_(n).

FIG. 8 shows a transmission scheme 800 with CDM applied across samples and symbols. A modulation symbol d may be sent on one set of N subbands in multiple symbol periods. The modulation symbol is replicated L times and multiplied with all L chips of the assigned spreading code to generate L scaled modulation symbols. For simplicity, FIG. 8 shows the case in which L is an integer multiple of N, and the modulation symbol is sent in L/N symbol periods. Modulation symbol d is multiplied with the first N chips c₁ through c_(N) of the assigned spreading code to obtain N scaled modulation symbols s₁=d·c₁ through s_(N)=d·c_(N) for the first SC-FDMA symbol, multiplied with the next N chips c_(N+1) through c_(2N) to obtain N scaled modulation symbols s_(N+1)=d·c_(N+1) through s_(2N)=d·c_(2N) for the second SC-FDMA symbol, and so on, and multiplied with the last N chips c_(L−N+1) through c_(L) to obtain N scaled modulation symbols s_(1−N+1)=d·c_(L−N+1) through s_(L)=d·c_(L) for the last SC-FDMA symbol. An SC-FDMA symbol may be generated for each sequence of N scaled modulation symbols.

To recover modulation symbol d sent across symbols and samples, the receiver multiplies the L scaled modulation symbols received for that modulation symbol with the L chips of the assigned spreading code. The receiver then accumulates the L resultant symbols to obtain a received modulation symbol for modulation symbol d.

FIGS. 5 through 8 show various schemes for applying CDM in the time domain. Other schemes for applying CDM in the time domain may also be implemented, and this is within the scope of the invention. For example, CDM may be applied across samples in only a portion of an SC-FDMA symbol, e.g., the first L samples of the SC-FDMA symbol. As another example, CDM may be applied across symbols for some sample indices and not applied for other sample indices. As yet another example, CDM may be applied on multiple modulation symbols, and each modulation symbol may be sent across both samples and symbols.

CDM may also be applied across subbands in the frequency domain. D modulation symbols may be sent on one set of N subbands in one symbol period, where D≧1 and D may or may not be an integer divisor of N. A D-point DFT may be performed on the D modulation symbols to obtain D frequency-domain values. Each frequency-domain value is then replicated L times, and the L replicated values are multiplied with the L chips of the assigned spreading code to generate L scaled values. A total of N scaled values are obtained for the D frequency-domain values and are mapped onto the N subbands used for transmission. Zero values are mapped onto the remaining subbands. A K-point IDFT is then performed on the K scaled and zero values to generate K time-domain output samples. An SC-FDMA symbol is formed by appending a cyclic prefix to the K output samples. CDM across subbands is similar to CDM across samples shown in FIG. 7, albeit with the vertical axis representing subband (instead of sample period) and d₁ through d_(N/L) representing the D frequency-domain values (instead of modulation symbols).

For CDM across subbands, the wireless channel is assumed to be static over the L subbands used to transmit a frequency-domain value, which are the subbands on which the L-chip spreading code is applied. To recover the D modulation symbols, the receiver obtains K+C input samples for the SC-FDMA symbol, removes the cyclic prefix, performs a K-point DFT on K input samples to obtain K received values, and retains N received values for the N subbands used for transmission. The receiver then multiplies the L received values for each transmitted frequency-domain value with the L chips of the spreading code, and accumulates the L resultant values to obtain a received frequency-domain value for the transmitted frequency-domain value. The receiver then performs a D-point IDFT on D received frequency-domain values to obtain D received modulation symbols.

In general, CDM may be applied in the time domain (e.g., as shown in FIGS. 5 through 8) or in the frequency domain. Applying CDM in the time domain may result in a lower peak-to-average power ratio (PAPR) than applying CDM in the frequency domain.

A transmitter may perform scrambling on the scaled and/or unscaled modulation symbols. Each transmitter may be assigned a scrambling code that is pseudo-random with respect to the scrambling codes assigned to other transmitters. Transmitter m may multiply each (scaled or unscaled) modulation symbol with a chip of an assigned scrambling code S_(m) prior to SC-FDMA modulation. The scrambling randomizes the interference caused by transmitter m to other transmitters transmitting on the same time-frequency block. The scrambling also allows the receiver to estimate the interference from other cells based on the unassigned spreading codes (e.g., if different sectors use different scrambling codes, and all transmitters within a sector use the same scrambling code), as described below. Scrambling may be performed on all types of data, on certain types of data, on data sent with CDM, and so on.

In the description above, the SC-FDMA symbols for different types of data have the same duration, and each SC-FDMA symbol is transmitted in K+C sample periods. SC-FDMA symbols of different durations may be generated for different types of data.

FIG. 9 shows a transmission scheme 900 with different symbol durations for different types of data. For transmission scheme 900, an SC-FDMA symbol for traffic data is composed of N_(T) output samples that are transmitted in N_(T) sample periods, an SC-FDMA symbol for signaling is composed of N_(S) output samples that are transmitted in N_(S) sample periods, and an SC-FDMA symbol for pilot is composed of N_(P) output samples that are transmitted in N_(p) sample periods, where N_(T), N_(S), and N_(P) may each be any integer value. For example, N_(T) may be equal to K+C, N_(S) may be equal to K/M_(S)+C, and N_(P) may be equal to K/M_(P)+C, where M_(S) and M_(P) may each be any integer value. As an example, a shortened SC-FDMA symbol for pilot may have half the duration of a normal SC-FDMA symbol for traffic data (not counting the cyclic prefix). In this case, there are K/2 total “wider” subbands for pilot, with each wider subband having twice the width of a “normal” subband for traffic data. As a specific example, K may be equal to 512, C may be equal to 32, N_(T) may be equal to K+C=544, N_(S) may be equal to K/2+C=288, and N_(P) may also be equal to K/2+C=288. An SC-FDMA symbol with N_(T), N_(S), or N_(P) output samples may be generated, e.g., as shown in FIG. 3A.

For LFDMA, a shortened SC-FDMA symbol and a normal SC-FDMA symbol may occupy the same portion of the system bandwidth. For IFDMA, there is no direct mapping between the wider subbands for a shortened SC-FDMA symbol and the normal subbands for a normal SC-FDMA symbol, for a given interlace. N wider subbands may be formed with multiple interlaces and divided into multiple subsets of wider subbands, which may be allocated to multiple transmitters assigned to these interlaces. Each transmitter may generate a shortened IFDMA symbol with the modulation symbols mapped onto the assigned subset of wider subbands.

CDM may be applied to SC-FDMA symbols of different durations. For the example shown in FIG. 9, a shortened SC-FDMA symbol may be generated for pilot and sent using CDM in L shortened symbol periods to reduce the amount of overhead of pilot. A shortened SC-FDMA symbol may also be generated for signaling and sent using CDM in L shortened symbol periods. Traffic data may be sent using normal SC-FDMA symbols.

In general, CDM may be applied to any type of data, e.g., traffic data, signaling, and/or pilot. For example, CDM may be applied to signaling and pilot but not traffic data, as shown in FIG. 6. As another example, CDM may be applied to signaling (e.g., for a control channel), but not traffic data or pilot. CDM may also be applied to a portion of a time slot (as shown in FIG. 6) or across an entire time-frequency block (e.g., as shown in FIG. 5). CDM may also be selectively applied, e.g., applied under poor channel conditions and not applied under good channel conditions.

CDM may improve reliability for a transmission sent in poor channel conditions. A transmitter may be constrained by a certain maximum transmit power level, which may be imposed by regulatory bodies or design limitations. In this case, a CDM transmission scheme allows the transmitter to transmit an SC-FDMA symbol over a longer time interval. This allows the receiver to collect more energy for the SC-FDMA symbol, which enables the receiver to perform detection at a lower SNR and/or derive a higher quality channel estimate. CDM may also whiten the interference caused to other transmitters, which may improve performance for these other transmitters.

FIG. 10 shows a process 1000 for transmitting SC-FDMA symbols with CDM. Modulation symbols for traffic data, signaling, and pilot are generated (block 1012). CDM is performed with an assigned spreading code C_(m) on the modulation symbols for traffic data, signaling, and/or pilot (block 1014). CDM may be performed for symbol periods used by multiple transmitters for transmission. CDM may also be performed across symbols, across samples, across both samples and symbols, across subbands, and so on. Scrambling may be performed with an assigned scrambling code S_(m) after the spreading (block 1016). SC-FDMA symbols of the same or different durations are generated for traffic data, signaling, and pilot (block 1018) and transmitted to the receiver.

FIG. 11 shows a process 1100 for receiving SC-FDMA symbols transmitted with CDM. SC-FDMA symbols are received for traffic data, signaling, and pilot sent by multiple transmitters (block 1112). Data transmitted with CDM may be separately recovered for each transmitter. The processing for one transmitter m may be performed as follows. SC-FDMA demodulation is performed to obtain received symbols for transmitter m (block 1114). Descrambling is performed (if applicable) on the received symbols with the scrambling code S_(m) assigned to transmitter m (block 1116). Despreading is performed on SC-FDMA symbols sent with CDM based on the spreading code C_(m) assigned to transmitter m (block 1118). An interference estimate may be derived based on the spreading codes not assigned to any transmitter (block 1120). A channel estimate may be derived for transmitter m based on a received pilot for the transmitter (block 1122). The channel estimate and interference estimate may be used for data detection (e.g., equalization), receiver spatial processing, and so on (block 1124). For example, coherent or non-coherent data detection may be performed for signaling sent with CDM, and receiver spatial processing may be performed for traffic data sent without CDM.

The receiver may derive an interference estimate during symbol periods in which CDM is applied. If L spreading codes are available and Q spreading codes are assigned to the transmitters, where Q<L, then the receiver may derive the interference estimate based on the L−Q unassigned spreading codes. For example, one or more spreading codes may be reserved for interference estimation and not assigned to any transmitter. For symbol periods in which CDM is applied, the receiver performs despreading with each of the Q assigned spreading codes to recover the transmissions sent by the transmitters. The receiver may also perform despreading with each of the L−Q unassigned spreading codes to obtain an interference estimate for that unassigned spreading code. For CDM across symbols, the interference estimate for an unassigned spreading code may be derived as follows:

$\begin{matrix} {{N_{j} = {\frac{1}{N \cdot L}{{\sum\limits_{n = 1}^{N}\;{\sum\limits_{i = 1}^{L}\;{{r\left( {t_{i},n} \right)} \cdot c_{i,j}}}}}^{2}}},} & {{Eq}\mspace{14mu}(2)} \end{matrix}$ where

r(t_(i), n) is a received symbol for sample period n in symbol period t_(i);

c_(i,j) is the i-th chip of the j-th unassigned spreading code; and

N_(j) is an interference estimate for the j-th unassigned spreading code.

Equation (2) despreads and accumulates the received symbols across L symbol periods t₁ through t_(L) and further averages the results across N sample periods. The receiver may average the interference estimates for all L−Q unassigned spreading codes to obtain an average interference estimate {circumflex over (N)}₀, as follows:

$\begin{matrix} {{\hat{N}}_{0} = {\frac{1}{L - Q} \cdot {\sum\limits_{j = 1}^{L - Q}\;{N_{j}.}}}} & {{Eq}\mspace{14mu}(3)} \end{matrix}$

The receiver may also derive an interference estimate for CDM across samples and CDM across both samples and symbols. In general, the receiver may despread across samples and/or symbols in a manner complementary to the spreading performed by the transmitter and may then accumulate the despread results across the samples and/or symbols.

The receiver may average the interference estimate across samples, symbols, and/or subbands in a given time-frequency block to obtain a short-term interference estimate. The receiver may also average the interference estimate across multiple time-frequency blocks to obtain a long-term interference estimate. The receiver may use the short-term interference estimate for channel estimation, data detection, receiver spatial processing, and so on. The receiver may use the long-term interference estimate to ascertain the operating conditions and/or for other purposes

For channel estimation, the receiver obtains a received SC-FDMA symbol for each symbol period used for pilot transmission by a given transmitter. The receiver may remove the cyclic prefix from the received SC-FDMA symbol, perform SC-FDMA demodulation, descrambling and despreading, and obtain received pilot values for the subbands used for pilot transmission. The received pilot values may be expressed as: R _(p)(k)=H(k)·P(k)+N(k), for kεK _(p),  Eq (4) where

P(k) is a transmitted pilot value for subband k;

H(k) is a complex gain for the wireless channel for subband k;

R_(p) (k) is a received pilot value for subband k;

N(k) is the noise and interference for subband k; and

K_(p) is the set of subbands used for pilot transmission.

The receiver may estimate N(k) based on the unassigned spreading codes, e.g., as described above. Alternatively, N(k) may be assumed to be additive white Gaussian noise (AWGN) with zero mean and a variance of N₀.

The receiver may estimate the frequency response of the wireless channel using a minimum mean-square error (MMSE) technique or some other technique. For the MMSE technique, the receiver may derive an initial frequency response estimate for the wireless channel, as follows:

$\begin{matrix} {{{\hat{H}(k)} = \frac{{R_{p}(k)} \cdot {P^{*}(k)}}{{{P(k)}}^{2} + {\hat{N}}_{0}}},{{{for}\mspace{14mu} k} \in K_{p}},} & {{Eq}\mspace{14mu}(5)} \end{matrix}$ where Ĥ(k) is a channel gain estimate for subband k and “*” denotes a complex conjugate. If |P(k)|=1 for all values of k, then equation (5) may be expressed as:

$\begin{matrix} {{{\hat{H}(k)} = \frac{{R_{p}(k)} \cdot {P^{*}(k)}}{1 + {\hat{N}}_{0}}},{{{for}\mspace{14mu} k} \in {K_{p}.}}} & {{Eq}\mspace{14mu}(6)} \end{matrix}$ The receiver may also derive a channel estimate in other manners.

For data detection, the receiver obtains a received SC-FDMA symbol for each symbol period used for data transmission by the transmitter. The receiver may remove the cyclic prefix from the received SC-FDMA symbol, perform SC-FDMA demodulation, descrambling and despreading, and obtain received data values for the subbands used for data transmission. The received data values may be expressed as: R _(d)(k)=H(k)·D(k)+N(k), for kεK _(d),  Eq (7) where

D(k) is a transmitted data value for subband k;

R_(d) (k) is a received data value for subband k; and

K_(d) is the set of subbands used for data transmission.

The receiver may perform data detection (or equalization) in the frequency domain on the received data values using the MMSE technique, as follows:

$\begin{matrix} {{{Z_{d}(k)} = \frac{{R_{d}(k)} \cdot {{\hat{H}}^{*}(k)}}{{{\hat{H}(k)}}^{2} + {\hat{N}}_{0}}},{{{for}\mspace{14mu} k} \in K_{d}},} & {{Eq}\mspace{14mu}(8)} \end{matrix}$ where Z_(d) (k) is a detected data value for subband k. Equation (8) is for data detection for one antenna. For multiple antennas, the receiver may derive a spatial filter matrix based on (1) the channel estimates for all transmitters transmitting in the same symbol period and (2) possibly the interference estimate. The receiver may then perform receiver spatial processing based on the spatial filter matrix to obtain the detected data values for each transmitter. The detected data values for all data subbands may be transformed with an IDFT/IFFT to obtain data symbol estimates.

FIG. 12 shows an embodiment of transmitter 110 m. Within TX data and pilot processor 120 m, an encoder 1212 encodes traffic data based on a coding scheme selected for traffic data. An interleaver 1214 interleaves or reorders the coded traffic data based on an interleaving scheme. A symbol mapper 1216 maps the interleaved data bits to modulation symbols based on a modulation scheme selected for traffic data. An encoder 1222 encodes signaling based on a coding scheme selected for signaling. An interleaver 1224 interleaves the coded signaling based on an interleaving scheme. A symbol mapper 1226 maps the interleaved signaling bits to modulation symbols based on a modulation scheme selected for signaling. A pilot generator 1232 generates modulation symbols for pilot, e.g., based on a polyphase sequence having good temporal characteristics (e.g., a constant time-domain envelope) and good spectral characteristics (e.g., a flat frequency spectrum). A multiplexer (Mux) 1238 multiplexes the modulation symbols for traffic data, signaling, and pilot onto the appropriate sample periods and symbol periods.

TX CDM processor 122 m performs spreading for CDM and scrambling. Within a CDM spreader 1240, a repetition unit 1242 repeats modulation symbols to be sent with CDM. A multiplier 1244 multiplies the replicated symbols with the L chips of an assigned spreading code C_(m) and provides scaled modulation symbols. The same or different spreading codes may be used for different types of data. A multiplexer 1246 receives the unsealed modulation symbols from processor 120 m and the scaled modulation symbols from CDM spreader 1240, provides the unsealed modulation symbols if CDM is not applied, and provides the scaled modulation symbols if CDM is applied. A multiplier 1248 multiplies the modulation symbols from multiplexer 1246 with an assigned scrambling code S_(m) and provides processed modulation symbols.

Within controller/processor 140 m, an FH generator determines the set of subbands to use for transmission in each time slot, e.g., based on a hop pattern assigned to transmitter 110 m. SC-FDMA modulator 130 m generates SC-FDMA symbols for traffic data, signaling, and pilot such that the modulation symbols are sent on the assigned subbands.

FIG. 13 shows an embodiment of SC-FDMA demodulator 160, RX CDM processor 162, and RX data processor 164 at receiver 150 for data sent with CDM. For simplicity, FIG. 15 shows the processing to recover the data sent by one transmitter m.

Within SC-FDMA demodulator 160, R SC-FDMA demodulators 1310 a through 1310 r receive the input samples from R demultiplexers 156 a through 156 r, respectively. Each SC-FDMA demodulator 1310 performs SC-FDMA demodulation on its input samples and provides received symbols. Within RX CDM processor 162, R multipliers 1318 a through 1318 r obtain the received symbols from SC-FDMA demodulators 1310 a through 1310 r, respectively. For each receive antenna, multiplier 1318 multiples the received symbols with the scrambling code S_(m) assigned to transmitter m. A CDM despreader 1320 performs despreading for transmitter m. Within CDM despreader 1320, a multiplier 1322 multiplies the descrambled symbols from multiplier 1318 with the spreading code C_(m) assigned to transmitter m. An accumulator 1324 accumulates the output of multiplier 1322 over the length of the spreading code and provides despread symbols. A CDM despreader 1330 performs despreading for each unassigned spreading code. An interference estimator 1332 derives an interference estimate for each unassigned spreading code, e.g., as shown in equation (2).

Within RX data processor 164, a data combiner 1340 combines the despread symbols across the R receive antennas. An interference combiner 1342 combines the interference estimates across the R receive antennas, e.g., as shown in equation (3). Combiner 1340 and/or 1342 may perform maximal ratio combining (MRC) and may give more weight to symbols with greater reliability, e.g., symbols with less interference. A data detector 1344 performs non-coherent detection for the data symbols sent with CDM. Although not shown in FIG. 13, RX data processor 164 may also perform deinterleaving and decoding if interleaving and encoding, respectively, are performed by transmitter m for the data sent with CDM.

FIG. 14 shows an embodiment of RX spatial processor 170. R DFT units 1410 a through 1410 r receive the input samples from R demultiplexers 156 a through 156 r, respectively. Each DFT unit 1410 performs a DFT on the input samples for each symbol period to obtain frequency-domain values for that symbol period. R demultiplexers/channel estimators 1420 a through 1420 r receive the frequency-domain values from DFT units 1410 a through 1410 r, respectively. Each demultiplexer 1420 provides frequency-domain values for data (or received data values) to K subband spatial processors 1432 a through 1432 k.

Each channel estimator 1420 performs descrambling and despreading on the frequency-domain values for pilot (or received pilot values), if the pilot was transmitted with scrambling and CDM, respectively. Each channel estimator 1420 derives a channel estimate for each transmitter based on the received pilot values for that transmitter. A spatial filter matrix computation unit 1434 forms a channel response matrix H(k,t) for each subband in each time slot based on the channel estimates for all transmitters using that subband and time slot. Computation unit 1434 then derives a spatial filter matrix M(k,t) for each subband of each time slot based on the channel response matrix H(k,t) and using zero-forcing (ZF), MMSE, or MRC technique. Computation unit 1434 provides K spatial filter matrices for the K subbands in each time slot.

Each subband spatial processor 1432 receives the spatial filter matrix for its subband, performs receiver spatial processing on the received data values with the spatial filter matrix, and provides detected data values. A demultiplexer 1436 maps the detected data values for each transmitter onto detected SC-FDMA symbols. A detected SC-FDMA symbol for a given transmitter is an SC-FDMA symbol that is obtained by receiver 150 for that transmitter with the interference from the other transmitters suppressed via the receiver spatial processing. SC-FDMA demodulator 172 processes each detected SC-FDMA symbol and provides data symbol estimates to RX data processor 174. SC-FDMA demodulator 172 may perform IDFT/IFFT, equalization, demapping of the data symbol estimates from the assigned subbands, and so on. SC-FDMA demodulator 172 also maps the data symbol estimates for the M transmitters onto M streams based on the traffic channels assigned to these transmitters. An FH generator within controller 180 determines the subbands used by each transmitter based on the hop pattern assigned to that transmitter. RX data processor 174 symbol demaps, deinterleaves, and decodes the data symbol estimates for each transmitter and provides the decoded data.

For the embodiment shown in FIG. 14, the receiver processing includes receiver spatial processing and SC-FDMA demodulation. The receiver spatial processing operates on frequency-domain values. The SC-FDMA demodulation includes the DFT/FFT performed by DFT units 1410 on the input samples to obtain frequency-domain values and the IDFT/IFFT performed by SC-FDMA demodulator 172 on the detected data values to obtain data symbol estimates. The receiver spatial processing and SC-FDMA demodulation may also be performed in other manners.

The techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units at a transmitter may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, electronic devices, other electronic units designed to perform the functions described herein, or a combination thereof. The processing units at a receiver may also be implemented with one or more ASICs, DSPs, processors, and so on.

For a software implementation, the techniques may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory (e.g., memory 142 or 182 in FIG. 1) and executed by a processor (e.g., controller 140 or 180). The memory unit may be implemented within the processor or external to the processor.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. 

The invention claimed is:
 1. A method of wireless communication, comprising: generating N modulation symbols for control information; spreading the N modulation symbols for the control information with a length L spreading code to obtain L sequences of N spread modulation symbols; generating L single-carrier frequency division multiple access (SC-FDMA) symbols based on the L sequences of N spread modulation symbols and a set of contiguous subcarriers used for transmission; and transmitting the L SC-FDMA symbols on the set of contiguous subcarriers across L symbol periods in a time slot assigned for transmission of the control information.
 2. The method of claim 1, further comprising: scrambling the N modulation symbols with a scrambling code prior to the spreading.
 3. The method of claim 1, further comprising: determining different sets of subcarriers to use for transmission in different time slots based on a frequency hopping pattern.
 4. A method of wireless communication, comprising: generating a single modulation symbol for control information; spreading the single modulation symbol for the control information with a length L spreading code to obtain L spread modulation symbols; mapping the L spread modulation symbols to a set of L contiguous subcarriers; generating a single single-carrier frequency division multiple access (SC-FDMA) symbol based on the L spread modulation symbols mapped to the set of L contiguous subcarriers; and transmitting the single SC-FDMA symbol on the set of L contiguous subcarriers in a time slot assigned for transmission of the control information.
 5. The method of claim 4, wherein the spreading comprises spreading the single modulation symbol across the set of L contiguous subcarriers and across multiple symbol periods.
 6. The method of claim 4, further comprising: determining different sets of subcarriers to use for transmission in different time slots based on a frequency hopping pattern.
 7. An apparatus for wireless communication, comprising: means for generating N modulation symbols for control information; means for spreading the N modulation symbols for the control information with a length L spreading code to obtain L sequences of N spread modulation symbols; means for generating L single-carrier frequency division multiple access (SC-FDMA) symbols based on the L sequences of N spread modulation symbols and a set of contiguous subcarriers; and means for transmitting the L SC-FDMA symbols on the set of contiguous subcarriers across L symbol periods in a time slot assigned for transmission of the control information.
 8. The apparatus of claim 7, further comprising: means for scrambling the N modulation symbols with a scrambling code prior to the spreading.
 9. The apparatus of claim 7, further comprising: means for determining different sets of subcarriers to use for transmission in different time slots based on a frequency hopping pattern.
 10. An apparatus for wireless communication, comprising: means for generating a single modulation symbol for control information; means for spreading the single modulation symbol for the control information with a length L spreading code to obtain L spread modulation symbols; means for mapping the L spread modulation symbols to a set of L contiguous subcarriers; means for generating a single single-carrier frequency division multiple access (SC-FDMA) symbol based on the L spread modulation symbols mapped to the set of L contiguous subcarriers; and means for transmitting the single SC-FDMA symbol on the set of L contiguous subcarriers in a time slot assigned for transmission of the control information.
 11. The apparatus of claim 10, wherein the means for spreading spreads the single modulation symbol across the set of L contiguous subcarriers and across multiple symbol periods.
 12. The apparatus of claim 10, further comprising: means for determining different sets of subcarriers to use for transmission in different time slots based on a frequency hopping pattern.
 13. A device for wireless communication, comprising: a processor; and a memory in electronic communication with the processor, the memory comprising instructions executable by the processor to: generate N modulation symbols for control information; spread the N modulation symbols for the control information with a length L spreading code to obtain L sequences of N spread modulation symbols; generate L single-carrier frequency division multiple access (SC-FDMA) symbols based on the L sequences of N spread modulation symbols and a set of contiguous subcarriers; and transmit the L SC-FDMA symbols on the set of contiguous subcarriers across L symbol periods in a time slot assigned for transmission of the control information.
 14. The device of claim 13, wherein the memory further comprises instructions executable by the processor to: scramble the N modulation symbols with a scrambling code prior to the spreading.
 15. The device of claim 13, wherein the memory further comprises instructions executable by the processor to: determine different sets of subcarriers to use for transmission in different time slots based on a frequency hopping pattern.
 16. A device for wireless communication, comprising: a processor; and a memory in electronic communication with the processor, the memory comprising instructions executable by the processor to: generate a single modulation symbol for control information; spread the single modulation symbol for the control information with a length L spreading code to obtain L spread modulation symbols; map the L spread modulation symbols to a set of L contiguous subcarriers; generate a single single-carrier frequency division multiple access (SC-FDMA) symbol based on the L spread modulation symbols mapped to the set of L contiguous subcarriers; and transmit the single SC-FDMA symbol on the set of L contiguous subcarriers in a time slot assigned for transmission of the control information.
 17. The device of claim 16, wherein the memory further comprises instructions executable by the processor to spread the single modulation symbol across the set of L contiguous subcarriers and across multiple symbol periods.
 18. The apparatus of claim 16, wherein the memory further comprises instructions executable by the processor to: determine different sets of subcarriers to use for transmission in different time slots based on a frequency hopping pattern.
 19. A non-transitory computer-readable medium storing computer executable code, the computer executable code comprising instructions for: generating N modulation symbols for control information; spreading the N modulation symbols for the control information with a length L spreading code to obtain L sequences of N spread modulation symbols; generating L single-carrier frequency division multiple access (SC-FDMA) symbols for transmission based on the L sequences of N spread modulation symbols and a set of contiguous subcarriers used for transmission; and transmitting the L SC-FDMA symbols on the set of contiguous subcarriers across L symbol periods in a time slot assigned for transmission of the control information.
 20. A non-transitory computer-readable medium storing computer executable code, the computer executable code comprising instructions for: generating a single modulation symbol for control information; spreading the single modulation symbol for the control information with a length L spreading code to obtain L spread modulation symbols; mapping the L spread modulation symbols to a set of L contiguous subcarriers; generating a single single-carrier frequency division multiple access (SC-FDMA) symbol based on the L spread modulation symbols mapped to the set of L contiguous subcarriers; and transmitting the single SC-FDMA symbol on the set of L contiguous subcarriers in a time slot assigned for transmission of the control information. 